Universality in edge-source diffusion dynamics

We show that in edge-source diffusion dynamics the integrated concentration N(t) has a universal dependence with a characteristic time-scale tau=(A/P)^2 pi/(4D), where D is the diffusion constant while A and P are the cross-sectional area and perimeter of the domain, respectively. For the short-time dynamics we find a universal square-root asymptotic dependence N(t)=N0 sqrt(t/tau) while in the long-time dynamics N(t) saturates exponentially at N0. The exponential saturation is a general feature while the associated coefficients are weakly geometry dependent.Comment: 4 pages including 4 figures. Minor changes. Accepted for PR

Best combiners during 40 years of breeding Vitis cuitivars resistant to Pierce's disease

By breeding for resistance to Pierce's disease in Vitis we have obtained useful cultivars that can be grown productively in areas formerly considered unsuitable for grape production. Reviewing the most successful recombinants from crosses made between 1945 and 1984, 6 Vitis clones were prominent foundation parents among those tested as primitive resistant germplasm: V. aestivalis, ssp. smalliana cvs Fla. 43-47 and Fla. 449, V. aestivalis ssp. simpsoni cvs Pixiola and Fla. 451, and V. shuttleworthii cvs Haines City and Kissimmee. The best combiners for productivity, fruit size, and high quality were PD susceptible cultivars Aurelia, Carolina Blackrose, Cardinal, Exotic, Golden Muscat, and Villard blanc. The best combiners for seedlessness and early ripening were susceptible cultivars Lakemont and Perlette. Selection for resistance to PD required 7 or more years each generation for exposure of seedlings to PD-carrying vectors. Inbreeding was detrimental to vine vigor but good combiners were selected among inbred progeny which were more homozygous for disease resistance. Subsequent crosses of these inbreds to large-fruited, high-quality cultivars resulted in some recombinants with restored vigor and superior traits such as Blanc Du Bois

Transport coefficients for electrolytes in arbitrarily shaped nano and micro-fluidic channels

We consider laminar flow of incompressible electrolytes in long, straight channels driven by pressure and electro-osmosis. We use a Hilbert space eigenfunction expansion to address the general problem of an arbitrary cross section and obtain general results in linear-response theory for the hydraulic and electrical transport coefficients which satisfy Onsager relations. In the limit of non-overlapping Debye layers the transport coefficients are simply expressed in terms of parameters of the electrolyte as well as the geometrical correction factor for the Hagen-Poiseuille part of the problem. In particular, we consider the limits of thin non-overlapping as well as strongly overlapping Debye layers, respectively, and calculate the corrections to the hydraulic resistance due to electro-hydrodynamic interactions.Comment: 13 pages including 4 figures and 1 table. Typos corrected. Accepted for NJ

Slow-light enhanced optical detection in liquid-infiltrated photonic crystals

Slow-light enhanced optical detection in liquid-infiltrated photonic crystals is theoretically studied. Using a scattering-matrix approach and the Wigner-Smith delay time concept, we show that optical absorbance benefits both from slow-light phenomena as well as a high filling factor of the energy residing in the liquid. Utilizing strongly dispersive photonic crystal structures, we numerically demonstrate how liquid-infiltrated photonic crystals facilitate enhanced light-matter interactions, by potentially up to an order of magnitude. The proposed concept provides strong opportunities for improving existing miniaturized absorbance cells for optical detection in lab-on-a-chip systems.Comment: Paper accepted for the "Special Issue OWTNM 2007" edited by A. Lavrinenko and P. J. Robert

Levitated droplet dye laser

We present the first observation, to our knowledge, of lasing from a levitated, dye droplet. The levitated droplets are created by computer controlled pico-liter dispensing into one of the nodes of a standing ultrasonic wave (100 kHz), where the droplet is trapped. The free hanging droplet forms a high quality optical resonator. Our 750 nL lasing droplets consist of Rhodamine 6G dissolved in ethylene glycol, at a concentration of 0.02 M. The droplets are optically pumped at 532 nm light from a pulsed, frequency doubled Nd:YAG laser, and the dye laser emission is analyzed by a fixed grating spectrometer. With this setup we have achieved reproducible lasing spectra in the visible wavelength range from 610 nm to 650 nm. The levitated droplet technique has previously successfully been applied for a variety of bio-analytical applications at single cell level. In combination with the lasing droplets, the capability of this high precision setup has potential applications within highly sensitive intra-cavity absorbance detection.Comment: 6 pages including 3 figure

Frequency response in surface-potential driven electro-hydrodynamics

Using a Fourier approach we offer a general solution to calculations of slip velocity within the circuit description of the electro-hydrodynamics in a binary electrolyte confined by a plane surface with a modulated surface potential. We consider the case with a spatially constant intrinsic surface capacitance where the net flow rate is in general zero while harmonic rolls as well as time-averaged vortex-like components may exist depending on the spatial symmetry and extension of the surface potential. In general the system displays a resonance behavior at a frequency corresponding to the inverse RC time of the system. Different surface potentials share the common feature that the resonance frequency is inversely proportional to the characteristic length scale of the surface potential. For the asymptotic frequency dependence above resonance we find a 1/omega^2 power law for surface potentials with either an even or an odd symmetry. Below resonance we also find a power law omega^alpha with alpha being positive and dependent of the properties of the surface potential. Comparing a tanh potential and a sech potential we qualitatively find the same slip velocity, but for the below-resonance frequency response the two potentials display different power law asymptotics with alpha=1 and alpha~2, respectively.Comment: 4 pages including 1 figure. Accepted for PR

A real-space grid implementation of the Projector Augmented Wave method

A grid-based real-space implementation of the Projector Augmented Wave (PAW) method of P. E. Blochl [Phys. Rev. B 50, 17953 (1994)] for Density Functional Theory (DFT) calculations is presented. The use of uniform 3D real-space grids for representing wave functions, densities and potentials allows for flexible boundary conditions, efficient multigrid algorithms for solving Poisson and Kohn-Sham equations, and efficient parallelization using simple real-space domain-decomposition. We use the PAW method to perform all-electron calculations in the frozen core approximation, with smooth valence wave functions that can be represented on relatively coarse grids. We demonstrate the accuracy of the method by calculating the atomization energies of twenty small molecules, and the bulk modulus and lattice constants of bulk aluminum. We show that the approach in terms of computational efficiency is comparable to standard plane-wave methods, but the memory requirements are higher.Comment: 13 pages, 3 figures, accepted for publication in Physical Review